phys O 2/3

Class Guidelines

  • Students are encouraged to review materials before class starts.

  • A few minutes before class begins, students must tuck items in their backpacks and clear aisles.

Wave Dynamics

Wave Height and Wind Influence

  • Wind plays a crucial role in wave formation.

  • As wind speed increases, potential wave height also increases.

  • This potential for wave growth is dependent on the distance the wind has traveled over water, known as fetch.

Fully Developed Sea

  • A fully developed sea contains waves of varying heights.

  • There are two categories of deepwater waves:

    • Wind waves: Generated by local winds.

    • Swell: Waves that have traveled away from their origin.

Wave Classification

  • Rather than using the average wave height, we use the significant wave height, which is the average of the highest third of waves.

  • Historical records show humans struggle to accurately estimate wave heights; thus, significant wave height provides a more standardized measure.

Shallow Water Waves

Wave Speed and Energy Conservation

  • The equation for shallow water wave speed is given by:

    • C = √(g d), where g is the acceleration due to gravity and d is the water depth.

  • As the wave enters shallower water, wave speed decreases while wave height must increase to conserve energy flux:

    • Energy Conservation Relation: C₁ h₁² = C₂ h₂²

    • This relationship shows that as speed decreases (C₂ < C₁), height must increase (h₂ > h₁).

Impact on Wavelength

  • The wavelength calculation for shallow water waves is given by

    • C = L/T (where L is wavelength and T is period).

  • If wave speed decreases and period remains constant, then:

    • L must change, reflecting a shift towards perpendicular orientation relative to the shore.

Wave Refraction

  • As waves approach the shore, they refract or change direction, influenced by depth variations, leading to phenomena like longshore drift.

  • Understanding the principles behind wave refraction is crucial for studying sediment transport and coastal erosion.

Erosion and Sediment Transport

Laboratory Observations

  • Students previously conducted labs simulating wave effects on sediment in environments resembling beaches.

  • Observations include:

    • Gentle waves lead to sediment settling.

    • High-energy waves (e.g., during storms) cause increased erosion as they pick up sand.

  • Seasonal wave patterns can create cycles of sand loss and replenishment on beaches.

Resonance in Ocean Basins

Definition and Scale

  • Resonance occurs when specific conditions create constructive interference at certain wavelengths, leading to amplified wave heights.

  • Natural and resonant periods dictate how waves behave in different basins.

Calculating Resonance Periods

  • For shallow water waves, the relationship of wavelength can be expressed as follows:

    • C = L/T, derived adjustments can provide an understanding of how to fit wavelengths into specific basin lengths.

  • For open basins:

    • First order resonance occurs at one-quarter wavelength compared to a closed basin.

  • Wavelengths can be explored using water depth and basin length measurements to determine resonant periods.